The smallest living cell is :
(a) Virus
(b) Viroid
(c) Mycoplasma
(d) Cyanobacteria

Options

A. Virus
B. Viroid
C. Mycoplasma
D. Cyanobacteria

Answer

To determine the smallest living cell among the given options, let's analyze each one step by step.

### Step 1: Understand the options
- **(a) Virus**: Viruses are not considered living cells because they cannot reproduce on their own and require a host cell to replicate. Therefore, they do not qualify as living organisms.

- **(b) Viroid**: Viroids are infectious agents composed of a short strand of circular RNA. They do not have a cellular structure and are also not considered living cells.

- **(c) Mycoplasma**: Mycoplasma are a group of bacteria that lack a cell wall. They are known to be the smallest living cells, with sizes around 0.0001 millimeters (or 100 nanometers). They can reproduce independently and are considered living organisms.

- **(d) Cyanobacteria**: Cyanobacteria are photosynthetic bacteria that are larger than mycoplasma. They are not the smallest living cells.

### Step 2: Compare the options
From the analysis:
- Viruses and viroids are not classified as living cells.
- Mycoplasma is the smallest living cell.
- Cyanobacteria are larger than mycoplasma.

### Step 3: Conclusion
Based on the information above, the smallest living cell is **(c) Mycoplasma**.

### Final Answer:
**(c) Mycoplasma**

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